Separation of mixtures of alkali metal nitrates with ammonium chloride



Patented July 24, 1934 UNITED STATES PATENT OFFICE METAL NITBATES CHLORIDE Friedrich Nessler, Berlin, Germany,

WITH AMMONIUM assignor to I. G. Farbenindustrie Aktiengesellschaft, Frankfort-on-the-Main,

Germany No Drawing. Application June 9, 1933, Serial No.

675,090. In Germany May 23, 1930 Claims.

The present invention relates to improvements in the separation of mixtures of alkali metal nitrates with ammonium chloride.

For the purpose of separating mixtures of I alkali metal nitrates with ammonium chloride such as are obtained for example in the conversion of alkali metal chlorides with ammonium nitrate, several processes have already been proposed. In particular it has been suggested to 10 separate the salt mixtures by an elutriation process or also to separate the salts by sieving them in the wet state.

I have now found contrary to expectation that salt mixtures composed of alkali metal nitrate and ammonium chloride can be separated into their components by subjecting them to a flotation treatment after adding flotation agents, the ammonium chloride passing into the froth and the alkali metal nitrate remaining unaltered at the bottom of the flotation vessel. In this process the salt mixtures to be treated are preferably suspended in the mother liquid resulting from the double decomposition of alkali metal chloride with ammonium nitrate. It is surprising that a flotation process can be carried through in this case because hitherto it was known only to separate by flotation water-insoluble substances from other water-insoluble substances as for example to separate ore from gangue.

The process in accordance with the present invention may be carried out for example as follows, it being understood, however, that the conditions of working may be varied within wide limits: The salt mixtures consisting of alkali metal nitrate and ammonium chloride which may be prepared in the known manner from alkali metal chloride and ammonium nitrate in an aqueous medium are subjected to flotation in a sufficient amount of aqueous liquid which initially need not be saturated with regard to the two salts, and the specific gravity of which is lower than that of each of the two salts, with an addition of a flotation agent as for example a so-called foaming agent or a collecting agent or a mixture of such agents. The production of froth may be effected in any suitable manner as for example by mechanical stirring or by introducing a diffused current of air or other gas under pressure or by the aid of currents of liquid or by means of a vacuum or also by spraying the liquid under treatment. Preferably a combination of several of the said methods is used as for example mechanical stirring while blowing through air. For producing the effect of flotation, the so-called oils used in the flotation of ores and also organic compounds which are either only collecting agents or only frothing agents or which possess both properties, either alone or in admixture with each other, have proved suitable. The ammonium chloride is conveyed to the surface together with the froth whereas the alkali metal nitrate remains at the bottom of the container from which it may be withdrawn.

For carrying out the process according to the present invention use may be made of one of the flotation apparatus known for the flotation of ores which, if necessary, may be suitably adapted to the requirements of the process in accordance with the present invention. The destruction of the froth for the purpose of recovering the ammonium chloride may be effected in any suitable manner as for example by spraying thereon water or alkaline liquids. The following method of working has proved to be particularly suitable for this purpose: The froth is suspended in a strong solution of ammonium chloride or in the liquid used for the double decomposition or the liquid withdrawn from the flotation apparatus and then stirred slowly. Thereby the so-called oil collects at the top in view of its lower specific gravity whereas the ammonium chloride separates at the bottom. This separation of oil is improved still further by the use of elevated temperatures. The ammonium chloride thus obtained may be subjected once more to the same treatment whereby the last portions of the flotation agents are removed from the salt. The flotation agents recovered in this manner may be reintroduced into the process. If desired the alkali metal nitrate may be subjected to a similar treatment for the removal of oil while using a strong alkali metal nitrate solution, for example potassium nitrate solution which may also contain the ions of ammonium, chlorine and sodium. The salts obtained in this manner are of a surprisingly high degree of purity.

The process .in accordance with the present invention may also be carried out continuously for example by removing the alkali metal nitrate collecting at the bottom of the flotation apparatus by means of a worm conveyor, whereas the ammonium chloride is withdrawn at the surface together with the froth.

The liquid used for the flotation process as well as that used for the treatment of the froth may be re-introduced into the process at any desired place, for example it may be used over again for the same operation. It may also be used for the conversion of further quantities of alkali metal chloride with ammonium nitrate and in this case any flotation agents which may still be present do not cause any inconveniences. The flotation process as well as the conversion of alkali metal chloride with ammonium nitrate may be carried out if desired in an acid or alkaline medium.

For the purpose of obtaining salts of nearly 100 per cent purity it is particularly advantageous to work in counter current in several apparatus, whereby the alkali metal nitrate which has not been completely freed from ammonium chloride in the first apparatus is conveyed into a second flotation apparatus, the nitrate then being freed from any oil which adheres thereto in any suitable manner, if desired. The froth resulting from the second apparatus after having taken up the last portions of the ammonium chloride present in the alkali metal nitrate admitted into this apparatus is conveyed into the first apparatus and is then caused to separate from the ammonium chloride taken up in one or two treatments for the removal of oil.

It may be advisable to avoid a substantial excess of the so-called oil in order to prevent small quantities of alkali metal nitrate from passing into the froth. However, in many cases the separation of the salt mixtures can be carried out with a particularly high efllciency by employing considerable amounts of flotation agents instead of the small quantities of these agents ordinarily used.

Generally speaking the froth obtained in the process according to the present invention is of a nature different from that of the froth obtained in ordinary flotation processes. A too strong formation of froth may be counteracted by suitably guiding the current of air or by suitably stirring or by maintaining the most favorable temperature. Even when using large quantities of oil the separation of the crystals or of the mother liquor does not offer any difficulties. In this case of the mother liquor a complete separation of the oil is not essential because the said liquor is always reintroduced into the operation. In the case of the ammonium chloride it is sumcient to warm the mixture of ammonium chloride, mother liquor and oil while slightly stirring. The bubbles of the froth may also be caused to burst and the particles of oil caused to combine, by other means such as the application of reduced pressure. In the same manner the alkali metal nitrate to which only small quantities of oil adhere be rendered free from oil.

The new process has substantial advantages over the old elutriation process. Thus the degree of purity of the alkali metal nitrates is substantially higher and this is essential for the fertilizer industries in view of the fact that even compartively small difl'erences in the degree of purity are regarded as important. In comparison therewith the removal of the oils which may adhere to the ammonium chloride, which removal is by no means necessary in all cases, is only of subordinate importance.

The following examples will further illustrate the nature of this invention which however is not restricted to these examples. The parts are by weight.

Example 1 A mixture of about equimolecular proportions of sodium nitrate and ammonium chloride obtained by the double decomposition of sodium chloride with ammonium nitrate is subjected to flotation while using the mother liquor from the double decomposition as the flotation medium and adding oleic acid and a little cresol, by vigorously stirring and passing through air.

The froth together with part of the aqueous Example 2 A conversion liquid which is to be used in circulation is prepared so as to have at 20 C. a composition about as follows: 1000 parts of water, 317 parts of potassium chloride, 182 parts of ammonium chloride and 300 parts of ammonium nitrate. This solution is saturated with regard to potassium nitrate and ammonium chloride. Equimolecular proportions of finely ground potassium chloride and ammonium nitrate are introduced into this liquid at 20 C. or at higher temperatures. The total amount of solid salts introduced is not essential, but preferably it is about one quarter to one third of the weight of the liquid used. The mixture is stirred well for several hours until the added solid salts are converted into an equivalent mixture of potassium nitrate and ammonium chloride, whereby solid salts are continuously present. The mixture thus prepared is subjected to flotation in the manner described in Example 1 whereby the ammonium chloride passes over with the froth whereas the potassiumnitrate is withdrawn from the flotation apparatus. After separating the mother liquor from the salts by centrifuging, the liquor is reintroduced into the process at any desired place for example for producing further amounts of the mixture of potassium nitrate and ammonium chloride or for separating mixtures of these salts which have already been prepared in another batch of solution.

Instead of the conversion liquid indicated above another liquid saturated with regard to potassium nitrate and ammonium chloride may be used, as for example a liquid composed of. 1000 parts of water, 403 parts of potassium chloride, 25 parts of ammonium chloride and 2000 parts of ammonium nitrate.

Example 3 A salt mixture obtained by the double decomposition of sodium chloride with ammonium nitrate and consisting of about equimolecular proportions of sodium nitrate and ammonium chloride together with the mother liquor is subjected to flotation while vigorously stirring or passing through air, after adding a viscous mineral oil such as a lubricating oil in an amount corresponding to 27 per cent by weight of the ammonium chloride present as the solid phase. The froth together with part of the aqueous liquid is introduced into a second container in which it is stirred slowly while warming to 60 C. The ammonium chloride crystals; collect at the bottom and are removed by means of a valve. After drying, the ammonium chloride is of 98.3 per cent purity. The sodium nitrate freed from ammonium chloride in the flotation apparatus and separated from the mother liquor is of 99 per cent purity.

'The aqueous medium used may also be rendered weakly alkaline as for example by the addition of ammonia.

What I claim is:-

1. The process of separating alkali metal nitrate from ammonium chloride which comprises subjecting a mixture of said alkali metal nitrate and ammonium chloride to froth flotation in an aqueous medium saturated with the said salts containing a flotation agent.

2. The process of separating alkali metal nitrate from ammonium chloride which comprises subjecting a mixture of said alkali metal nitrate and ammonium chloride to froth flotation in an aqueous medium saturated with the said salts containing a flotation agent, withdrawing the resulting froth, warming it, thereby separating ammonium chloride from the froth, and withdrawing alkali metal nitrate from the aqueous medium.

3. The process of separating alkali metal nitrate from ammonium chloride which comprises subjecting a mixture of said alkali metal nitrate and ammonium chloride to froth flotation in a mother liquid from the double decomposition of alkali metal chloride with ammonium nitrate, in'the presence of a flotation agent.

4. The process of separating alkali metal nitrate from ammonium chloride which comprises subjecting a mixture of said alkali metal nitrate and ammonium chloride to froth flotation in a mother liquid from the double decomposition of alkali metal chloride with ammonium nitrate, in the presence of a flotation agent withdrawing the resulting froth, warming it, thereby separating ammonium chloride from the froth, and withdrawing alkali metal nitrate from the mother liquid.

5. The process of separating potassium nitrate from ammonium chloride which comprises subjecting a mixture of said potassium nitrate and ammonium chloride to froth flotation in an aqueous medium saturated with the said salts containing a flotation agent.

6. The process of separating sodium nitrate from ammonium chloride which comprises subjecting a mixture of said sodium nitrate and ammonium chloride to froth flotation in an aqueous medium saturated with the said salts containing a flotation agent.

7. The process of separating potassium nitrate from ammonium chloride which comprises subjecting a mixture of said potassium nitrate and ammonium chloride to froth flotation in a mother liquid from the double decomposition of potassium chloride with ammonium nitrate, in the presence of a flotation agent.

8. The process of separating sodium nitrate from ammonium chloride which comprises subjecting a mixture of said sodium nitrate and ammonium chloride to froth flotation in a mother liquid from the double decomposition of sodium chloride with ammonium nitrate, in the presence of a flotation agent.

9. The process of separating potassium nitrate from ammonium chloride which comprises subjecting a mixture of said potassium nitrate and ammonium chloride to froth flotation in a mother liquid from the double decomposition of potassium chloride with ammonium nitrate, in the presence of a flotation agent withdrawing the resulting froth, warming it, thereby seperating ammonium chloride from the froth, and withdrawing potassium nitrate from the mother liquid.

10. The process of separating sodium nitrate from ammonium chloride which comprises subjecting a mixture of said sodium nitrate and ammonium chloride to froth flotation in a mother liquid from the double decomposition of sodium chloride with ammonium nitrate, in the presence of a flotation agent withdrawing the resulting froth, warming it, thereby separating ammonium chloride from the froth, and withdrawing sodium nitrate from the mother liquid.

FRIEDRICH NESSLER. 

